This invention relates to a low-cost energy-efficient vehicle air conditioning system including an electrically operated variable capacity refrigerant compressor and a manual driver interface.
Variable capacity refrigerant compressors have been utilized in both manual and automatic vehicle air conditioning systems, primarily to reduce engine load disturbances associated with compressor clutch cycling. In a typical implementation, the compressor includes one or more pistons coupled to a tiltable wobble plate or swash plate, and a pneumatic or electromagnetic control valve for adjusting the pressure in a crankcase of the compressor to control the compressor capacity. The system control strategy usually involves adjusting the compressor capacity to maintain a predetermined low-side refrigerant condition (refrigerant suction pressure or evaporator outlet air temperature, for example) that provides maximum cooling without evaporator icing, and using a high-side pressure switch to disengage the compressor clutch if the refrigerant discharge pressure becomes too high. The inlet air may consist of outside air or recirculated cabin air, and the temperature of the discharge air is typically controlled by adjusting a mechanism (such as an air mix door) that reheats a portion of the conditioned air.
While the above-described control strategy is simple and reasonably effective, it has been recognized that the energy efficiency of the system could be significantly improved by increasing the usage of recirculated cabin air and reducing the compressor capacity in a way that provides adequate dehumidification while minimizing reheating of the conditioned air. However, since energy-efficient controls typically require a number of external sensors for measuring system and ambient parameters, development efforts have primarily been focused on automatic systems that usually include such sensors anyway. Accordingly, what is needed is a low-cost energy-efficient air conditioning control system suitable for usage in a so-called manual system where the operator manually controls the discharge air temperature and inlet air source.
The present invention is directed to an improved energy-efficient vehicle air conditioning system including a variable capacity refrigerant compressor having a capacity control valve with integral refrigerant sensors and control circuitry. The system includes a driver interface panel for selecting the discharge air temperature and inlet air source, and for selecting either a normal control mode or an energy-efficient control mode. When the energy-efficient control mode is selected, control setting indicators prompt the driver to request full-cold discharge air temperature and recirculated cabin air, and the control circuitry initiates a compressor capacity control based on the refrigerant sensor information and a measure of the outside air temperature to produce a suitable discharge air temperature at a reduced power consumption level.
In a preferred embodiment, the capacity control valve includes suction and discharge pressure sensors, and the control circuitry selects a suction pressure target based on the outside air temperature and the sensed discharge pressure, and then adjusts the compressor capacity as required to attain the target suction pressure. Alternatively, the outside air temperature and sensed discharge pressure may be used to select a target evaporator outlet air temperature, which is compared with a measure of the actual evaporator outlet air temperature to produce a target suction pressure.